Over the last decade or so, the use of cyclonic separating apparatus to separate particles from an airflow in a vacuum cleaner has been developed and introduced to the market. Detailed descriptions of cyclonic separating apparatus for use in vacuum cleaners are given in, inter alia, U.S. Pat. No. 3,425,192, U.S. Pat. No. 4,373,228 and EP 0 042 723. From these and other prior art documents, it can be seen that it is known to provide two cyclone units in series so that the airflow passes sequentially through at least two cyclones. This allows the larger dirt and debris to be extracted from the airflow in the first cyclone, leaving the second cyclone to operate under optimum conditions and so effectively to remove very fine particles in an efficient manner. This type of arrangement has been found to be effective when dealing with airflows in which is entrained a variety of matter having a wide particle size distribution, as is the case in vacuum cleaners.
Some arrangements have been proposed in which the downstream cyclone has been replaced by a plurality of downstream cyclones arranged in parallel. Examples are shown in U.S. Pat. No. 3,425,192 and JP S52-014774. In both of these arrangements, the downstream cyclones are housed within a casing which surrounds the cyclones so that the volume occupied by the cyclones is not minimised.